1. Field of the Invention
This invention relates to a liquid-sealed vibration-proof device used for supporting and bearing a vibration generator mainly such as automobile engines, etc. in a vibration-isolating manner.
2. Description of the Related Art
As a mount for supporting and bearing a vibration generator, e.g. automobile engine, etc. so as not to transmit its vibration to the vehicle body, there is known a liquid-sealed type of vibration-proof device.
Such vibration-proof device is comprised of a cylindrical main body fitting to be attached and fastened to the support side, e.g., the vehicle body frame, an upper fitting to be attached to the vibration generator side,. e.g., engine, a thick-walled vibration-insulating base made of rubber material and assuming a generally truncated cone configuration interconnecting the main body fitting and the upper fitting, a diaphragm provided opposite to the vibration-insulating base at the lower side of the main body fitting, and a liquid-sealed chamber enclosed between the vibration-insulating base, and the diaphragm, the liquid-sealed chamber including two liquid sub-chambers on the base side and the diaphragm side divided by a partition, both sub-chambers communicating through an orifice with each other thereby exhibiting a fluid flow effect between both sub-chambers through the orifice, so that a vibration damping function and a vibration insulating function are performed.
Other ones falling under the aforementioned type of vibration-proof device are also known such that the partition is further provided in its center with a rubber-like elastomer membrane for closing openings in order that vibration damping effect may be attained in a different frequency band or a wide range of frequency bands, or the partition is provided with a movable plate having a valve function to through-holes.
The vibration-proof devices fitted with the elastic membrane or mobile plate above, however, have posed the problems that the elastic membrane has limits in vibrational amplitude of elastic deformation and as such has its limitations in reduction of the dependency on vibrational amplitude, or that the mobile plate impinges strongly on the stopper for limiting the movement of the mobile plate in a wide area of it to generate abnormal or strange sound.
Therefore in order to solve the problems with the vibration-proof device stated above, the present inventors have formerly proposed such a construction that the partition dividing the interior into a main liquid chamber and a subsidiary liquid chamber comprises an orifice member having at its outer circumference an orifice channel, a partition member provided in contact with the lower side of the orifice member and supporting the orifice member between it and the vibration-insulating base, and a rubber-like elastomer membrane interposed between both members and having an open end sliding movable to the inner surface of the orifice member (PCT/JP01/02718).
This invention is designed to further improve the aforesaid vibration-proof device as proposed on the configuration and supporting structure of the rubber-like elastomer membrane, and to provide a liquid-sealed vibration-proof device with which it is possible to preclude generation of abnormal sound, to reduce the dependency on vibration amplitude, to exhibit a vibration-proof effect over a considerably wide rage of frequency bands ranging from low frequency band to medium and high frequency bands, and to fabricate the device in a light weight configuration at inexpensive cost.
Accordingly, this invention is, in generic terms, concerned with a liquid-sealed vibration-proof device comprising a vibration-insulating base as a vibration-proof device proper, a diaphragm opposed thereto, a liquid-sealed chamber enclosed between the vibration-insulating base and the diaphragm, the chamber including a main liquid chamber on the vibration-insulating base side and a subsidiary liquid chamber on the diaphragm side partitioned, and a partition having an orifice for putting both chambers into communication with each other. And the device is characterized in that the partition comprises an orifice member including an annular wall section having an orifice channel defined at its outer circumference and a central plate section having a plurality of openings; a partition plate member provided in contact with a lower side of the orifice member to support the orifice member between it and the vibration-insulating base; and a rubber-like elastomer membrane disposed within a space between the central plate section of the orifice member and the partition plate member, the rubber-like elastomer membrane including a central plate-form portion held by and pinched between the orifice member and the partition plate member, and a diaphragm portion extending outwardly of the central plate-form portion and having at its outer circumference an open end, the open end.being brought into pressure contact with an inner peripheral surface of the annular wall section of the orifice member in a sliding movable manner; and openings are provided at such positions that the central plate section of the orifice member and the partition plate member pinch and hold the central plate-form portion of the rubber-like elastomer membrane between them, the central plate-form portion being partly exposed at the openings to the main liquid chamber and the subsidiary liquid chamber, thus being formed as an elastic membrane capable of elastic deformations.
According to this liquid-sealed vibration-proof device, the diaphragm portion of the rubber-like elastomer membrane of the partition is slidingly movable to the inner circumferential surface of the annular wall section of the orifice member, thus capable of sliding displacing depending on a pressure difference between the main and subsidiary liquid chambers; and furthermore, part of the central plate-form portion held by and between the central plate section of the orifice member and the partition plate member is exposed to both the main chamber. and subsidiary chamber and is capable of elastic deformation due to a liquid difference between both chambers. Hence it is possible to minimize the dependency on vibrational amplitude and to reduce the dynamic spring rate over a considerably wide range of frequency bands from medium to high frequency band. Upon vibration in a low frequency and large vibrational amplitude, the open end of the diaphragm portion of the rubber-like elastomer membrane, abuts on the inner surface of the orifice member and the partition plate member thereby inhibiting further sliding displacement and accordingly, the liquid flows through the orifice located at the outer cirumference of the partition, whereby a high damping can be attained. Consequently, a good vibration-isolating effect can be exhibited over a wide range of frequency bands.
Furthermore, the diaphragm portion of the rubber-like elastomer membrane in a cantilevered state slides, at its open end, toward the inner peripheral surface of the annular wall section of the orifice member and comes to abut on the partition plate member from the open end. Thus the prior art defect with the mobile plate having a valve function that it impinges on the stopper for limiting its movement in a wide area is avoided and generation of abnormal sound (hitting sound) can be reduced.
In addition, because of the fact that the rubber-like elastomer membrane is adjacent to and held to be pinched by the central plate section of the orifice member and the partition plate member without vulcanization bonding to both, reinforcing fittings required when vulcanization bonding the rubber-like elastomer membrane are dispensed with. As a consequence, it is possible to reduce the number of component pieces, to fabricate the device easily and at inexpensive cost, and to make it lightweight.
In the liquid-sealed vibration-proof device described above, a structure of the rubber-like elastomer membrane in its supporting state will be specifically stated: The central part of the partition plate member assumes a projecting portion inboard of the annular wall section of the orifice member, and between the projecting portion and the annular wall section, an annular space is thus formed. The rubber-like elastomer membrane is positioned, with the thick-walled lower annular wall of the central plate-form portion thereof fitted and seated on the projecting portion at its outer periphery, and the diaphragm portion can be arranged within the annular space so as to be sliding movable. Thereby the rubber-like elastomer membrane can be securely and stably pinched and fixed in place between the central plate section of the orifice member and the partition plate member without any deviation.
In the device described above, the central plate section of the orifice member and the partition plate member are provided with openings communicating respectively with the diaphragm portion within the space so that liquid pressures of the main liquid chamber and the subsidiary liquid chamber can act on the diaphragm portion of the rubber-like elastomer membrane.
It is preferred in the liquid-sealed vibration-proof device above that the elastic membrane part at the central plate-form portion of the rubber-like elastomer membrane should assume a projecting shape so as to be fitted in the opening of the orifice member. This is because the state of the rubber-like elastomer membrane being pinched and held can be stabilized.
Preferably the annular wall section of the orifice member bulges out at its inner peripheral surface inwardly toward the lower side of the central plate section, assuming a radius or curvature, and the diaphragm portion of the rubber-like elastomer membrane has a curved contour conforming nearly to the radius curvature. In particular, it is further desirable that the open end of the diaphragm portion extend to the proximity, of a corner area formed by the inner surface of the annular wall section and the upper surface of the partition plate member. The effect of preventing the generation of abnormal sound which attends on the displacement of the diaphragm portion is thus improved.
When the open end of the diaphragm portion of the rubber-like elastomer membrane is formed thin-walled, a sufficient contact area with the annular wall section of the orifice member can be assured, whereby it is possible to shut off positively between the main and subsidiary liquid chambers without leakage of liquid. This is more preferable in exhibiting a required vibration damping function.